The instant invention is directed to degassing a liquid using a membrane contactor.
The use of membrane contactors for degassing of liquid is known. See, for example, U.S. Pat. No. 5,938,922; Japanese Patent Nos. 2,725,311, 2,743,419, and 2,949,732; and commercially available products traded under the name of Separel(copyright) hollow fiber membrane degassing modules from Dainippon Ink and Chemicals, Inc. of Tokyo, Japan, and Liqui-Cel(copyright) membrane contactors from Celgard Inc. of Charlotte, N.C.
U.S. Pat. No. 5,938,922 discloses a contactor with a baffle to direct liquid flow in a specific path. Note FIG. 2 of U.S. Pat. No. 5,938,922, liquid passes radially from the core, over the membranes (where gas is diffused into the lumen), around the baffle in longitudinal direction, radially inward to the core, and exits the contactor via the core. Vacuum is drawn on the lumen side of the polypropylene homogeneous microporous hollow fiber membrane, and liquid is introduced within the shell of the contactor via the perforated core. While this contactor is capable of obtaining less than 1 ppb of dissolved gas at the pressure range of 15 to 20 torr, it is difficult to manufacture.
Japanese Patent No. 2,725,311 discloses a contactor for degassing liquids with a non-homogeneous hollow fiber membrane made from poly(4-methylpentene-1) or PMP. Non-homogeneous membranes are distinguished from porous membranes (e.g. microporous membranes).
Japanese Patent No. 2,743,419 discloses a contactor for degassing a liquid which is able to discharge a liquid with less than 300 ppb dissolved gas, but the liquid temperature must be elevated to about 40 to 80xc2x0 C., and the vacuum level is at 30 to 100 torr.
Japanese Patent No. 2,949,732 discloses a contactor for degassing using a non-homogeneous PMP hollow fiber membrane and a sweep gas or a combination of vacuum and sweep gas. Liquids can be degassed to around 500 ppb at flow rates of 7 to 8.3 liters per minute (lpm) and at vacuum pressures in the range of 28 to 38 torr.
Separel(copyright) EF 040P from Dianippon Ink and Chemical Inc. of Tokyo, Japan uses the skinned (non-communicating pore) PMP membrane mentioned above, has a radial flow pattern with a shell egress, and reports dissolved gas levels below 1 ppb but only at low flow rates (xe2x89xa620 liters per minute) with 40 m2 membrane area. At greater flow rates (33-57 lpm), dissolved gas levels range from 18-96 ppb.
Membrane contactors are useful in the following commercial applications: feeding oxygen for cultivating enzymes and microbes in medicine and foodstuff production; feeding oxygen in waste water treatment systems; oxidizing broths with air or ozone in chemical and pharmaceutical unit operations; feeding oxygen in fish breeding and transportation industries; feeding oxygen to culture solutions in hydroponic farming; preparing water having high oxygen contents for manufacturing face treating liquids and health beverages; eliminating one or more kinds of components contained in gases by dissolution into liquids (e.g. SOx, NOx, H2S, etc.), in waste gas cleaning and eliminating CO2 from fermented methane gas; degassing liquids, e.g. deoxidizing water fed to boilers and liquids fed to reverse osmosis membranes, to produce super-pure water for semi-conductor rinsing, deoxidizing water and seawater for mist prevention of pipes and refrigerators, to eliminate CO2 from biological cultures, to eliminate organic solvent from waste water; and to simultaneously dissolve and eliminate gases from liquid.
In the area of high purity water for rinsing semi-conductors, as the semi-conductors become more complex, the need for greater purity water (e.g.  less than 1 ppb dissolved oxygen) becomes greater.
The present invention is directed to degassing a liquid with a membrane contactor. A liquid having a dissolved gas is introduced into a contactor which is connected to a vacuum source. The contactor has a perforated core, a plurality of hollow fiber membranes, a tube sheet affixing each end of said fibers, and a shell having a liquid egress. The shell encloses the fibers, the tube sheet, and the core. The hollow fiber lumens are in fluid communication with the vacuum source. Liquid enters the contactor via the core""s open end radially exits the core, crosses over the membranes within the shell, and exits the contactor by the liquid egress. The dissolved gas thereby diffuses from the liquid across the membrane into the lumen. The liquid exiting may have a dissolved gas content to less than 1 ppb.